The present invention relates in general to a printer; and, more particularly, the invention relates to a printer that is capable of reserving the sheet wrapping width onto photoconductors by use of very few wrapping members.
A printer for executing multi-color printing, while vertically conveying a form, such as a continuous web, has a constitution in which a plurality of drum photoconductors are arranged in a zigzag manner on both sides of the form, and toner images are alternately formed on the first side and second side of the form and then are fixed by a fixing unit, with the result that double-side multi-color printing is executed in one process. In this printer, the drum photoconductors are rotated by following the form, so that the form must be wrapped around the drum photoconductors with a fixed wrapping width, and a transfer section is installed in the neighborhood of the intersection point between a horizontal line passing through the center of the drum photoconductors and the form (for example, refer to Patent Document 1).
Further, the technique of reserving the fixed wrapping width of the form for the photoconductors, thereby increasing the transfer width and realizing a high image quality, is generally known.
On the other hand, for printing only on the first side of the form, as shown in FIG. 7, there is a known constitution in which, by use of a wrapping roller 108 installed on the second side of the form, a fixed wrapping width of the form for a drum photoconductor 101 is reserved. Even in such a constitution, a transfer unit 106 is installed in the neighborhood of the intersection point between a horizontal line LH passing through a center 101c of the drum photoconductor 101 and the form (for example, refer to Patent Document 2).
Further, there is a known constitution in which a first side printing section and a second side printing section are separately installed in one frame; and, after completion of printing on the first side, printing on the second side is executed. Namely, in this constitution, one-side printing is repeated at two steps in one frame, so that double-side printing is executed (for example, refer again to Patent Document 2).                Patent Document 1: Japanese Application Patent Laid-open Publication No. Hei 07-77851        Patent Document 2: Japanese Application Patent Laid-open Publication No. Hei 07-72776        